Circuit breaker



Oct. 10, 1939. R. s. TUSING CIRCUIT BREAKER Filed Jan. 30, 1957 2 Sheets-Sheet 1 INVENTOR Ray 5 705/72 BY WITNESSES: 4% 473M @XW ATTORNE 2 Sheets-Sheet 2 INVENTOR Roy J' 77/5/09. BY Z/ a) ATTORNE R. S. TUSING CIRCUIT BREAKER Filed Jan. ISO, 1937 Oct. 10, 1939.

Patented Oct. 10, 1939 PATENT OFFICE CIRCUIT BREAKER Roy S. Tusing, Turtle Creek, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 30, 1937, Serial No. 123,233

18 Claims.

My invention relates to circuit controlling devices in general and more particularly to trip devices for circuit breakers.

An object of my invention is to provide a circuit breaker having an improved trip mechanism capable of opening the breaker after a predetermined time interval in response to an'overload in the controlled circuit, and capable of opening the breaker immediately upon the occurrence of a short circuit condition in the controlled circuit. I

Another object of my invention is to provide a trip device for a circuit breaker embodying an improved thermally responsive trip means actuated by a snap-acting disk heated by metallic conduction from a current-carrying heater strip.

Another object of my invention is to provide a circuit breaker embodying an improved thermally responsive trip means which is provided with a simple adjusting means for varying the trip rating of the circuit breaker.

Another object of my invention is to provide an improved thermally responsive trip means for a circuit breaker that is simpler, more eflicient and reliable in operation than trip means of the same general type that have heretofore been known or used.

The novel features that I consider characteristic of my invention are set forth in particular in the appended claims. The invention itself, however, both as to structure and operation, together with additional objects and advantages thereof, will best be understood from the following detailed description of a specific embodiment thereof when read in connection with the accompanying drawings, in which:

Figure 1 is a plan view of a multipole circuit breaker embodying'th'e features of my invention,

the cover being broken away to illustrate certain details of the breaker;

Fig. 2 is a vertical sectional view of a portion of the circuit breaker illustrated in Fig. 1 taken on the line 11-11 of Fig. 1;

Fig. 3 is an enlarged central vertical sectional view of the trip device showing the thermally responsive trip means in the normal position;

Fig. 4 is a vertical sectional view of the trip device similar to Fig. 3 showing the thermally responsive trip means in the operative position toeflect a tripping operation of the breaker; and Fig. 5 is a fragmentary view taken on the line V-V of Fig. 3.

Referring to the drawings, the base I of the circuit breaker isof molded insulating material and has mounted thereon the end terminals 3 and 5, the unitary trip structure indicated generally at i, the circuit breaker operating mechanism 9 which has associated therewith the assembly of the switch members II and the arc extinguishers l3 which have integral therewith the main stationary contact I5 and the auxiliary stationary contact H. The switch members H and the stationary contacts l5 and I! combine to form a plurality of poles. Each of the poles of the circuit breaker is insulated from the adjacent pole by means of one of the insulating barriers l9, which are formed integral withthe base I. These insulating barriers iii are adapted to align with similar barriers (not shown) in the cover 2|, which is likewise of molded insulating material. The operating handle 23, which is rigidly afiixed to the switch operating mechanism 9, is also of molded insulating material and has a portion 25 which projects through a suitable opening 21 in the cover 2|.

The unitary trip device I has a base 29 and a cover 30, both'of molded insulating material. The unitary trip structure 1 fits in a suitable recess in the insulating base I of the breaker and is fastened therein, as will be described hereinafter, through the agency of suitable screw fastenings.

The electric circuitifor each of the poles of the breaker is substantially the same. Beginning with the terminal 3, the current passes successively through the arc extinguishing structure i3, the stationary contact IS, the moving contact 3| and the conducting shunt 33 associated with the switch member II, the unitary trip structure 1 the shunt 33 connecting with the terminal 35 of the trip deviceand thence through the trip structure to the other terminal 5. I

Each of the switch members II has a channelshaped frame 31 of iron upon which the movable contact is pivotally supported.- The moving contact 3! is pivotally fastened to the iron frame 31 by a pivot pin 39 which extends through two openings formed in the opposite sides of the frame 31. Two cotter pins 4| prevent the pivot pin 39 from moving out of position. The flexible shunt 33 is riveted to the moving contact 3| at one end, and at its other end is' provided with a terminal portion for engaging the corresponding terminal 35 of the trip structure 1; the screws 41, which engage suitable threaded recesses I! in the base I, being provided to releasably connect these terminals.

Each of the moving contacts 3| has a portion described in the application'of M. W. Brainard,

I extending rearwardly into the frame 31. This portion 5| isengaged by the free end of a spring 53; the other end of the spring 53 being rigidly fastened to the frame'31 by means of rivets 55.

' A square insulating tie-bar 51 extends across all three poles of the breaker. This bar is rigidly aflixed to the rearward portion of each of the switch members II by means of an iron strap 59 which loops about the bar 51 and has projections (not shown) which extend through suitable openings in the frame 31 and aretherein clenched. This bar serves to. rigidly connect all of the Serial No. 593,236, filedFebruary 16, 1932, and assigned to the 'assignee of this invention which became Patent No. 1,896,764 on February 7, 1933.

The operating mechanism comprises in general a U-shaped base or frame 63, a pair of toggle links 65 and 61 for engaging the assembly-of the switch members II, a releasable actuatin member 69 for releasably restraini the toggle links 65 and 61 in an operative position, a bifurcated operating lever 1I, overcenter springs 31 of the central switch member II.

13 for connecting the operating lever 1| to the knee of the toggle links, and the operating handle 23. The U-shaped frame 63 is fastened to the insulating base I of the circuit breaker by means of four screws, 14, two at either end. A pivot pin 11 extends through suitable openings in the'U-shaped frame 63 and engages the frame v This pin 11 provides a pivot point for the assembly of the switch members II, all of which are mechanically tied together by the insulating tie-bar 51. Other openings are provided in the base 63 for the reception of the pivot pins 19--one on either .side of the U--which provide ,pivot points for the bifurcated operating lever 1|. The lower end of the toggle link 61 is pivotally connected to the frame 31 of the central switch member II by the pivot pin 8|, the pin 8| serving to connect the operating mechanism 9 and the assembly of the switch members II. The other end of the toggle link 61 is pivoted at one end of the toggle link 65 by means of the knee pivot pin 93. The knee pivot pin has means associated therewith for engaging one end of each of the overcenter springs 13, one on either end, the other end of the overcenter springs being connected to the operating handle 23.

The actuating member 69, which is pivoted about the pin 85, provides a releasable restraining means for holding the toggle links 65-61 in the operable position; the other end of the toggle link 65 being pivotally secured to the actuating member 69 by the pin 99.

The movement of the bifurcated operating member H is limited by the inwardly extending projections 9| and 93 of the U-shaped frame adapted to be engaged by a latchmeans of the trip device 1 to restrain the actuating member 69 in its normal position.

The trip device 1 is entirely assembled on its own base 29 and is completely removable from the circuit breaker. The trip device includes a thermally responsive trip means indicated generally at 99, and a magnetically responsive trip means indicated generally at IOI for each of the three poles of the breaker. The mechanism of the device is so arranged that a moderate .or lower magnitude overload of predetermined duration in the circuit controlled by any one of the-poles will actuate the trip mechanism, and a heavier overload or short-circuit condition in the circuit controlled by any one of the poles will actuate the trip mechanism instantaneously to open ail three poles of the breaker.

Each of the magnetically responsive trip means is mounted on the base 29 by means of a frame I03. The frame I03 is substantially U-shaped, and has an upstanding bracket I05 secured thereto by rivets I01, which bracket functions to support the stationary U-shaped core I09 of the magnetically responsive trip means. Screw fastenings III extend through suitable openings in the. base 29 and serve to support each of the frames I03. A conductor H3 is provided for each of the trip means and comprises a strip of conducting material, preferably copper, having enlarged end portions which form the terminals 35 and 31 of the trip device. The conductor has a central portion I I5 of reduced area, or, which is the same thing, increased resistance, which forms a heat producing portion. The reduced portion is bent backward to form an inverted U-shaped loop about the U-shaped core I09 of the magnetically responsive means. Thus the current flowing in e conductor II3 energizes the magnetically responsive trip means. The U-shaped stationary core I09 is secured to the upstanding brackets I05 by means of a pair of rivets I I1, and is thereby positioned between the leg portions of the conductor H3. The core I09 of the magnetically responsive trip means provides the attracting means for the movable armatures II9. Each of the armatures II9 comprises a rectangular strip of magnetic material mounted by means of a guiding member I2I for slidin'gmovement on a pair of cylindrical guide rods I23 which are atfixed to the base 29 of the trip device,by means of screw fastenings I25. A biasing spring I21 is positioned about-each of the guide rods I23, and

provides a means for biasing the movable armature I I9 away from the stationary core I09. The biasing springs are retained in position on the guide rods by means of washers and cotter pins.

It is imperative for accurate operation that the trip device be positioned very accurately with respect to the path of movement of the end 95 of the releasable actuating member 69. In order to accomplish this accurate positioning, there is provided a metallic bracket I29 which is rigidly secured to the central portion of the trip base 29 by means of the central screw fastenings I25. The bracket I29 has a base portion which is of substantially the same outline as the central terminal 35, and is thus adapted to be fastened to the base I of the circuit breaker by means of central screw fastenings 41. The central screw fastenings 41 would probably be sufiicient to accurately position the trip base with respect to the operating mechanism 9, but in order to insure that the positioning is correct, there is provided an additional positioning means which con-, sists of a projecting male member I3I, which extends downwardly through a suitable opening in the central terminal of the trip device, and is adapted to engage a female portion I33 in the terminal and central shunt 33, this terminal and shunt being securely fastened to the base and accurately positioned with respect to the operating mechanism 9 by means of the screws I35.

The bracket I29 has,an opening I31 in the upper portion thereof for the reception of a pivoted latch I39, the latch being pivotally mounted in the opening through the agency of a pivot pin I. The latch I39 is preferably constructed of metal and has a projecting portion I43 for engaging the latch 91 associated with the end 95 of the releasable actuating member 69. A spring I45 is provided for biasing the latch I39 to the latched position, and a notch I41 is pro-- vided in the latch for engagement by a bracket I55 attached to the trip bar I 49. v

The trip bar I49 is of molded insulating material and extends across all three poles of the breaker. It is pivotally supported at either end through the engagement of pivot pins I5I with suitable openings in the trip bar itself. The pivot pins I5I are supported by brackets I53 (see Fig. 2) which are fastened to the ends of the trip base by means of screws (not shown).

The trip bar I49 engages the latch I39 through the agency of the bracket I55, one end of which engages the notch I41 in the latch I39 andthe other end of which is rigidly affixed to the trip bar by a pair of rivets I51. A compression spring I59 biases the trip bar in a clockwise direction about its pivot pin to its latched position. Three downwardly extending members I6 I, one for each pole of the breaker, are aflixed tothe trip bar by means of rivets, as shown. These downwardly extending members are provided for engaging the armatures II9 of each of the magnetically responsive trip means of the trip device.

The end portion 95 of the actuating member 69 includes a bifurcated projection which pivotally supports the latch 91. The latch 91 is biased into the engaged position by a spring I63, and its movement in a clockwise direction is limited by a portion of the bifurcated end of the actuating member 69. a

Each of the thermally responsive trip means, there being one for each pole of the breaker, comprises a snap-acting bimetal disc I65. The

disc I65 is of the type that passes from one to the other of its two oppositely flexed positions with a snap-action when heated or cooled a predetermined amount. The disc I65 is supported by means-of an adjusting screw I61. The adjusting screw passes through an opening I69 in one of the legs of the conducting member H3, and is provided with a threaded portion "I which threadedly engages a threaded opening I13 provided in the opposite leg of the conducting member 3.. The disc I 65 is provided with a central opening for mounting the same on a groove provided on the forward end of the adjusting screw I61, as best shown in Figs. 3 and 4. The screws I61 pass through openings provided therefor in the cover 39 of the trip device and are provided with knurled operating handles I15 for adjusting the initial position of the disc I65. Each of the discs I 65 is thus mounted with its edges in contact with the reduced or heat producing portion I I of the conductor strips II 3, whereby the discs are adapted to be heated by conduction from the conductor H3. The trip bar I49 is provided with a plurality of projections I11, one for each of the snap-acting bimetal discs. The projections I11 are adapted to be engaged and moved by the discs I65 when the discs have been heated a predetermined amount predetermined period of time, the snap-acting bimetal disc I65 on the pole in which the overload occurs is heated by the heat producing portion of its conducting s'trip II3. When the disc has been heated a predetermined amount, it snaps to its oppositely flexed position withlts edges away from the reduced portion II5 of its conductor strip I I3, as shown in Fig. 4. In passing to its oppositely flexed position, the edge of the disc engages the corresponding projection I11 on the trip bar I49 and moves the trip bar in a counterclockwise direction against the bias of the springs I59 to its tripped position to efi'ect release of the pivoted latch I39, resulting in a tripping operation of the breaker. When the disc has snapped to the position shown in Fig. 4 in response to a moderate overload, its edges are away from the reduced portion II5 of the conductor strip I I3 so that it cools quickly and snaps back to its original or normal position, as shown in Fig. 3.

The adjusting screw I61 provides a simple and efiective means for adjusting the trip rating of the thermal trip means. Turning the screw I61 in a counter-clockwise direction causes the edges of the bimetal disc I65 to engage the conductor I I3 with increased pressure, or what is more important, moves the central portion of the disc nearer its dead-center position, so that the disc will be heated the predetermined amount neces- /sary to cause it to snap over to its oppositely flexed position in response to an overload of lower predetermined magnitude, or causes the disc to respond to a moderate overload in a. shorter time. When the adjusting screw I61 is turned in,a clockwise direction, substantially the reverse action takes place; the contact pressure between the edges of the disc and the conductor strip H3 is reduced, or what is more important, the central portion of the disc is moved further away from the conductor strip so that it requires a greater amount of heat to cause the disc to snap over to itsoppositely flexed position. Under these conditions, it requires a greater overload for a given time interval to cause the disc to snap over to eflect a tripping operation, or a. lower overload for a greater period of time to cause the disc" are fully described in Patent No. 2,047,739, grant-\ ed H. J. Lingal, on July 14, 1936, and assigned to the assignee of this invention.

The operation of the circuit breaker is briefly as follows: To open the contacts manually, the

operating handle 23 is moved clockwise about its pivot 19, whereupon the overcenter springs 13 exert a force having a component tending to move the knee pivot pin 83 of the toggle mechanism toward the base 29 of the trip device or out of toggle. At a. certain point, this component of force exerted by the spring 13 becomes suflicient ,75

to cause the toggle to collapse, resulting in a clockwise movement of the switch members It about the pivot pin ll, thus opening the contacts of the breaker. The motion of the central switch member ii is transmitted to the outer switch members by the insulating tie-bar 5'! as has previously been pointed out. The closing operation is substantially the reverse or the opening operation, the knee of the toggle links bein moved by the overcenter springs in this case away from the base 29 of the trip device, or in toggle. The combination of the toggle mechanism and the overcenter springs connected to their knee pivot makes it possible to open and close the breaker contacts with a snap-action. The proportions of the moving contact 311 are such that the circuit is first made and finally interrupted through the amriliary contacts. When the brealrer is in the fully closed position, the auxiliary contacts are slightly separated and the circuit is completed through the main con tacts.

When the breaker is in the closed circuit posi tion, as shown in Fig. 2, and an overload oi nioderate magnitude and predetermined duration ocours in the circuit in any one oi the poles oi the breaker, the heat produced by the reduced portion or the conductor M3 oi the pole on which the overload occurs heats the snap-acting bimetallic disc ltd a swdicient amount to cause it to snap to its oppositely flexed position away from the conductor 8 it, as shown in Fig. 4. The snap-acting movement or the bimetal disc (1% causes the edge thereoi to engage the projection ill! of the trip bar M59, and move the trip bar in a counter-clockwise direction to its tripped position, as shown in Fig. The movement or the trip bar M9 to tripped position causes the bracket ltd carried by the trip bar to release the latch H35. The release of the latch i351 allows the actuating member to be moved in a counter-clockwise direction about its pivot pin 85 under'the biasing influence or the over-center springs it. At a predetermined point the coun terclockwise movement of the actuating mem= ber 69, the line of action of the overcenter springs 13 causes collapse of the toggle links to and bi resulting in an opening of the contacts of thebreaker in a manner previously described in connection with the manual operation.

The latch M9 returns to latching position under the influence of its biasing spring M5. Due to the fact that the circuits have been opened and that the bimetal disc has snapped to a position away from the reduced portion of the conductor H3, the disc I cools quickly and snaps back to its original position with its edges in gontact with the conductor H3. The return of the disc I65 to its original position allows the trip bar I49 to be returned to its normal position under the influence of the biasing springs I59, and the bracket I55 reengages 'thenotch I" in the latch I39. The trip device is thus automatically reset following each tripping operation. To reclose the breaker after a tripping operation, it is necessary to move the operating handleto the full open circuit position. In moving to the, full open circuit position a. projection I19 carried by the operating member engages and moves the spring biased actuating member 69 to its normal position, duringwhich the latch 91 reengages under the projection I43 of the latch I39. The

breaker is now completely reset and may be reclosed by manually moving the operating member 23 to the closed circuit position, during which the contacts are closed in the manner described in connection with the manual operation of the mechanism.

In the event of a short-circuit or very heavy magnitude overload in the circuit controlled byand moves the trip bar in a counterclockwise di-- rection to its tripping position to eifect release of the latch M9 and the actuating member till in the manner previously described in connection with the tripping operation efiected by the thermally responsive trip means.

lit will be noted that the conductor strips ili form the energizing means for both the magnetically responsive trip means and the thermally responsive trip means.

The provision oi the improved thermally responsive trip means comprising the snap-acting bimetal disc and the particular adjusting means provides a simpler, more reliable and more eflicient thermal trip means than has heretofore been known or used and the adjusting screw provides a simple means for accurately adjusting the thermal trip rating oi the breaker; The position or the snap=ucting bimetal disc with its edges in contact with the heat producing portion or the conductor provides for an emcient transfer or heat from the conductor to the thermally re-= sponsive trip element, by conduction; and the disc in snapping to its opposite position with its edges away from the heat producing portion oi the conductor strip allows the thermally responsive element to cool faster and snap back against the conductor ready tor the next operation.

Since the disc moves from one to the other of I vention in connection with a particular term of' circuit breaker, it is obvious that it is equally applicable to other terms of ,circuit breaker structures.

. While 1 have shown and described the invention in accordance with the provisions of the patent statutes, it is to be understood that various changes in the structural details thereof may be made without departing from the spirit of the invention. I desire, therefore, that the invention be limited only by the reasonable construction of the appended claims and by the prior art.

I claim as my invention: f

1. In a trip devicefor a circuit breaker, a conductor, and a snap-acting bimetal member mounted'with one part in heat conducting'relationship to said conductor and said part being movable upon the bimetal member reaching a given temperature to break said heat conducting relationship.

2. In a trip device for a circuit breaker, a conductor, and a snap-acting bimetal mounted with one part only in heat conducting relationship to said conductor, said member when heated a predetermined amount passing from one to the other of two oppositely flexed positions with a snapaction to eflect a tripping operation the breaker and to move said one part away from said conductor.

. 3. In a trip device for a circuit breaker, a current-carrying conductor, and a snap-acting thermostatic disc mounted with its edge portions only in contact with said conductor, said disc when heated a predetermined amount changing its position with a snap-action to efiect a tripping operation of said breaker and to move its edge portions away from said conductor.

4. In a trip device for a circuit breaker, a current-carrying conductor adapted to be connected in circuit with the contacts of said breaker, and a snap-acting thermostatic disc mounted with only one portion thereof in contact with said conductor, the remaining portions of said disc being disposed away from said conductor, said disc when heated a predetermined amount by said conductor snapping to an inverted position in which all portions thereof are away: from said conductor.

/ 5. Ina trip device for a circuit breaker, a current-carrying conductor adapted to be connected in circuit with the contacts of said breaker, and a snap-acting thermostatic disc mounted with only its edge portionsin contact with said conductor, said disc when heated a predetermined amount snapping to a position with its edges away from said conductor to eflect a tripping operation of the breaker.

6. In a trip device for a circuit breaker, a current-carrying conductor, a snap-acting bimetal disc mounted with its edges in contact with said conductor, and means for adjusting the position 01' said disc to vary the-trip rating of said device.

7. In a trip device for a circuit breaker, a current-carrying conductor having a heat producing portion, said conductor being adapted for connection in circuit with the contacts 01' said breaker, a snap-acting bimetal member, and means mounting said member with only one portion thereof in heat conductive relationship to said heat producing portion of said conductor, the other portions of said bimetal member being disposed away from said conductor, said bimetal member when heated a predetermined amount by the heat produced by said conductor snapping to an inverted position in which all portions thereof are away from said conductor.

8. In a trip device for a circuit breaker, a current-carryingconductor having a heat producing portion, said conductor being adapted for connection in circuit with the contacts of said breaker, a snap-acting bimetallic disc, and means mounting said disc with its edge portion only in contact' with said heat producing portion of said conductor, said disc when heated a predetermined amount snapping to an inverted position with its edge portion away from said conductor toeffect a tripping operation of saidbreaker.

9. In a trip devcice for a circuit breaker, a

current-carrying conductor, a snap-acting bimetal disc disposed with its edges in contact with said. conductor, and means for varying the contact pressure between the edges of said disc and said conductor to vary the trip rating of the deyice.

-10. In a trip device for a multipole circuit breaker, a trip bar extending across two or more poles of the breaker movable from a normal position to a tripping position to effect a circuit opening operation of the breaker, a plurality of electromagnetic trip means,one for each pole,

each operable in response to overloads of prea plurality of snap-acting bimetal discs, one for each pole, mounted with only one portion thereof in heat conducting relationship to they said increased resistance portions of the conductors,

each disc when heated a predetermined amount in response to lower magnitude overloads being 3 snapped to an inverted position with all portions thereof away from said conductor to move said trip bar to tripping position.

11. In a circuit breaker provided with relatively movablegcontacts, a tripping member mov- 5 able from a normal position to a tripped position to effect opening of said contacts, a conductor adapted to be connected in circuit with said contacts provided with a portion of increased resistance, electromagnetic trip means energized by said conductor operable upon the occurrence of an overload of more than a predetermined magnitude to move said tripping member to tripped position, and a snap-acting bimetal member mounted with only one portion thereof in heat conductive relationship to said increased resistance portion of'said conductor, said bimetal member being operable when heated a predetermined amount in response to overloads of lower magnitude to move with a snap action to a posi tion in which all portions thereof are away from said conductor to actuate said tripping member to tripped position.

12. In a. circuit breaker, relatively movable contacts, a tripping member movable from a 35 normal position to a tripping position to eilect opening of said contacts, a conductor adapted to be connected in circuit with said contacts and having a portion of increased resistance, electromagnetic trip means energizedby said conductor operable upon the occurrence of overloads of predetermined magnitude to move said tripping member to tripping position, a snap-actingbimetal disc mounted in heat conductive relationship to the increased resistance portion of said conductor, said disc when heated a predetermined amount in response to an overload of lower predetermined magnitude snapping from one to the other of its two flexed positions to efl'ect movement of said trip member'to tripping position, and means movable to adjust the trip characteristic of said bimetal disc.

13. In a circuit breaker having relatively movable contacts, a tripping member movable from a normal position to a tripping position to efl'ect opening of said contacts, a conductor adapted to be connected in circuit with said contacts and having a portion of increased resistance, electromagnetic trip means energized by said conductor operable upon the occurrence of overloads of pre- 6 determined magnitude to move said tripping member .to tripping position, a snap-acting bimetal member mounted in heat conducting relationship to the increased resistance portion of said conductor, said member when heated a prede- 66 opening of the contacts of the breaker, a conduc tor adapted to be connected in circuit with said contacts and having a portion of increased resist- .ance, electomagnetic trip means energized by said conductor operableupon the occurrence of overloads of predetermined magnitude to move said tripping member to tripping position, a snapacting bimetal disc mounted with its edge portions only in contact with the increased resist ance portion of said conductor, said disc when heated a predetermined amount in response to lower magnitude overloads snapping to an in= verted position in which all portions thereofare away from said conductor to cause movement of said tripping member to tripping position.

15. In a trip device for acircuit breaker having relatively movable contacts, a tripping member movable from a normal position to a tripping position to effect opening of the contacts of the breaker, a conductor adapted to be connected in circuit with said contacts and having a portion of increased resistance, electromagnetic trip means energized by said conductor operable upon the occurrence of overloads of predetermined magnitude to move said tripping member to tripping position, a snap-acting bimetal disc mounted with its edges in contact with the increased resistance portion of said conductor, said disc said actuating member, a conductor connected in circuit with said contacts, and a snap-acting bi= metallic member mounted with its edge portion only in contact with said conductor, said mem ber when heated a predetermined amount being snapped to an inverted position in which all'portions thereof are away from said conductor to effect release of said latch means to free said actuating member.

17.111 a multiple circuit breaker having a plurality of pairs of relatively movable contacts forming aplurality of poles, at common operating mechanism for simultaneously opening or closing all of said pairs of contacts, and a spring biased actuating member releasable to eflect simultaneous opening of all of said pairs of contacts, the combination of a trip device comprising releasable latch means for restraining said actuating member, a trip bar extending across two or more poles of said breaker biased to a normal position to restrain said latch means in latching position and movable to a tripping position to release said latch means to free said actuating member, a plurality of electromagnetic trip means one for each pole each operable upon the occurrence of overloads of predetermined magnitude in the circuit of its pole to move the trip bar to tripping position, an energizing conductor for each of said electromagnetic means connected in circuit with the contacts of its pole and having a portion of increased resistance, a plurality of snap-acting bimetal discs one for each pole each mounted with only one portion thereof in heat conductive relationship to the increased resistance portions of said conductors, each of said discs when heated a predetermined amount in response to lower magnitude overloads being snapped to aninverteol position inrwhich all portions thereof are away irom said conductor to cause movement of said trip bar to tripping position.

s 18. In a circuit breaker, a base, relatively movable contacts, operating mechanism for opening and for closing said contacts, a spring biased actuating member releasable to effect opening of said contacts a removable trip device comprising a base, a conductor strip secured to the trip base, releasably connectible at each end for mounting the trip base on the breaker base and for providing terminals for the trip device, a releasable latch means for restraining said actuating member, a snap-acting bimetal member mounted with only one portion thereof in heat conductive relationship to said conductor, said bimetal member when heated a predetermined amount by overload current flowing in said conductor snapping to a position in which all portions thereof are away from said conductor to eifect release of said latch means to free said actuating member.

, lEtQY S. TUSMG. 

